Nadir: Sounds to me like basic power supply B+ regulation has failed..... bad regulator chip, high esr electrolytics, shorted diodes, etc...... a common high failure part is the STK regulator but the other parts of the circuit must be tested. Put a meter on the regulated B+ rail and then vary the AC input voltage with a variac +/- 10 volts to see if the B+ holds steady. If the problem is not there, then look for faulty screen filtering caps .... usually low up/high voltage units near and around the flyback...... i.e.
22@250, etc.-- Best Regards, Daniel Sofie Electronics Supply & Repair
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I am currently working on an RCA 27" model F27634ET, chassis CTC187BJ.
> The original problem was the set would squeal when plugged in and
> wouldn't power on. Q401 was shorted B-E, I don't have a BUH517 on
> hand so I subbed with a BU2520DF. C4709 was also replaced and I
> resoldered the flyback, STK regulator, H-Out transformer and pretty
> much most of the deflection/PS section of the board. The set now runs
> and the HOT is warm to the touch but well below maximum temperature.
> However the picutre changes size dramatically with any change in
> brightness. If I turn the brightness down low the picture will shrink
> down by about 20% on all sides and there is some pincushion
> distortion. I suspected it may be the usual tuner solder problem but
> if i bring up a static picture and firmly tap the tuner the picture
> doesn't flinch. Pincushion problems are usually related to Q851,
> D851, C4803, C4402, C4403, CR4402, C4407 and CR4403 but here they all
> test OK. I suspect it may be the STK regulator module failing but I
> want to be sure before replacing it. Any help is appreciated.
> Thanks.